The explosive growth of globally-distributed computer networks, such as the Internet and broadband networks, the presence of relatively large storage devices and data archives, and the development of efficient compression standards have provided digital image producers and others with a variety of means for distributing their images and other productions. However, these advancements have also made it relatively simple for copyright violators and others to create illegal copies of these images and other productions. As a result, a variety of conventional digital watermarking methods have been proposed. A digital watermark encodes an owner's copyright and/or tracking information and embeds it into an image or other production. Preferably, this digital watermark is invisible to the human eye and may only be perceived by a computer or the like. Digital watermarking methods may be used to identify the owner of an image or other production, to track illegal copies of the image or other production, and to facilitate the licensing of the image or other production. For a digital watermarking method to be successful, the digital watermark must be unobtrusive and must not degrade the perceptual quality of the image or other production. The digital watermark must also be resistant to attacks from a variety of image and signal processing tools and techniques, both unintentional and intentional. Such attacks may include, for example, image compression, smoothing, low-pass filtering, cropping, geometric transformation (including translation, rotation, and scaling), noise addition, printing and scanning, and collusion.
In general, a digital watermark may be applied in either the spatial (pixel) domain or the transform domain. Transform domain digital watermarking methods, such as discrete cosine transform (DCT) and discrete wavelet transform (DWT) digital watermarking methods, typically provide relatively high image fidelity and are resistant to image manipulations. Wavelet-based digital watermarking techniques have multi-resolution hierarchical characteristics that mimic human visual (and audio) perception and allow for the independent processing of the resulting components. With wavelet-based digital watermarking techniques, digital watermark detection may be achieved at relatively low image resolutions, saving computational load. In addition, the high-frequency sub-bands of a wavelet transform include the edges and textures of an image and the human eye is typically insensitive to changes in such sub-bands. This allows digital watermark to be added to the sub-bands without being perceived by the human eye. Wavelets are used in a variety of emerging image and video compression standards, such as JPEG2000 and MPEG4, encouraging the use of wavelet-based digital watermarking. Although embodiments and examples of the present invention deal with transform-based imperceptible digital watermarking methods, the principles and techniques of the present invention are also applicable to spatial (time)-based imperceptible digital watermarking methods as well.
A variety of conventional wavelet-based digital watermarking methods have been proposed. All of these methods are designed to be resistant to a variety of attacks. Typically, these digital watermarking methods insert a digital watermark into the high-frequency contents of an image or other product. Although marginally effective with respect to some types of attacks, the conventional digital watermarking methods are vulnerable to attack if techniques such as low-pass filtering are used. In addition, the conventional digital watermarking methods tend to be labor-intensive, relatively slow, and lack the ability to be adequately automated.
Thus, what is needed is a digital watermarking method that embeds a digital watermark in both the low and high frequencies of an image or other production, providing a digital watermark that is resistant to a variety of attacks. This digital watermarking method should optimize the strength of the embedded digital watermark such that it is as powerful as possible without being perceptible to the human eye. The digital watermarking method should do this relatively quickly, in real-time, and in an automated fashion using an intelligent system, such as a neural network. The watermarking method should also be able to be used in a variety of new applications, such as the watermarking of sensitive aircraft parts, military equipment, and machines.